The present disclosure relates to powered fastener-driving tools. Generally, powered fastener-driving tools employ one of several types of power sources to drive a fastener (such as a nail or a staple) into a workpiece. More specifically, a powered fastener-driving tool uses a power source to drive a piston carrying a driver blade through a cylinder from a pre-firing position to a firing position. As the piston moves to the firing position, the driver blade travels through a nosepiece, which guides the driver blade to contact a fastener housed in the nosepiece. Continued movement of the piston through the cylinder toward the firing position forces the driver blade to drive the fastener from the nosepiece into the workpiece. The piston is then forced back to the pre-firing position in a way that depends on the tool's construction and the power source the tool employs. A fastener-advancing device forces another fastener from a magazine into the nosepiece, and the tool is ready to fire again.
Combustion-powered fastener-driving tools are one type of powered fastener-driving tool. A combustion-powered fastener-driving tool uses a small internal combustion engine as its power source. For a typical combustion-powered fastener-driving tool, when an operator depresses a workpiece-contact element of the tool onto a workpiece, one or more mechanical linkages cause: (1) a valve sleeve to move to seal a combustion chamber that is in fluid communication with the cylinder; and (2) a fuel delivery system to dispense fuel from a fuel canister into the (now sealed) combustion chamber.
The operator then pulls the trigger to actuate a trigger switch, thereby causing a spark plug to spark and ignite the fuel/air mixture in the combustion chamber. This generates high-pressure combustion gases that expand and force the piston to move through the cylinder from the pre-firing position to the firing position, thereby causing the driver blade to contact a fastener housed in the nosepiece and drive the fastener from the nosepiece into the workpiece. Just before the piston reaches the firing position, the piston passes exhaust ports defined through the cylinder, and some of the combustion gases that propel the cylinder exhaust through the ports to atmosphere. This combined with the fact that the combustion chamber remains sealed during firing generates a vacuum pressure above the piston and causes the piston to retract to the pre-firing position. When the operator removes the workpiece-contact element from the workpiece, a spring biases the workpiece-contact element from the firing position to the pre-firing position, causing the one or more mechanical linkages to move the valve sleeve to an unsealed position to unseal the combustion chamber.
Operation of a conventional combustion-powered fastener-driving tool can be adversely affected if the valve sleeve moves and the combustion chamber unseals before the piston returns to the pre-firing position. For instance, assume the operator removes the workpiece-contact element from the workpiece before the piston returns to the pre-firing position. This causes the valve sleeve to move to the unsealed position and unseal the combustion chamber. When this happens, the vacuum pressure is lost. This could cause the piston to stop moving before reaching the pre-firing position, which in turn could cause the tool to malfunction the next time the operator attempts to use the tool to drive a fastener.
Conventional combustion-powered fastener-driving tools typically include one of several types of lockout devices to ensure the valve sleeve doesn't move and the combustion chamber remains sealed until the piston returns to the pre-firing position. But while beneficial, these lockout devices add complexity to the tools, including mechanical and in some cases electromechanical components that are additional points of potential tool failure and increase manufacturing cost.
Since repeated use of conventional combustion-powered fastener-driving tools generates a significant amount of heat, the materials of some components of conventional combustion-powered fastener-driving tools are selected because they effectively conduct and dissipate heat. For instance, the cylinder and the valve sleeve are typically cast from an aluminum alloy, which is an efficient conductor. But while beneficial, these materials are heavy and can cause operator fatigue during extended tool operation.
There is a continuing need for a combustion-powered fastener-driving tool that effectively manages heat generated during extended use and that ensures that its piston returns to the pre-firing position after driving a fastener.